Standard optical systems having standard lenses have been developed around the assumption that a light emitter constitutes a point light source, having no width or diameter. As a result, the standard lens equation, the basis for all imaging optical design, is a simple equation that determines the curve of a standard lens. The standard lens equation is a function of the thickness of the lens, the distance (R) from the central axis of the lens, the radius of the curvature (roc) of the lens, the sign factor γ (gamma) having a value of 1 or −1 so as to indicate positive and negative radii of curvatures, respectively, and the conic constant (conic):
  zStandardLens  =      LensThickness    +                  roc        -                  γ          ⁢                                                    roc                2                            -                                                (                                      1                    +                    conic                                    )                                ⁢                                  R                  2                                                                                1        +        conic            
FIGS. 1a and 1b show the standard lens curve of the prior art. FIG. 1a shows an exemplary standard lens curve on a two-dimensional axis, having a LensThickness of 3 millimeters, an roc of −4 millimeters and a conic of 0.5. FIG. 1b shows a standard lens 11 according to the curve of FIG. 1a, having lines of curvature 12. It is well known in the field that the lens of an optical device can be manufactured with refraction or absorption characteristics that are a function of the wavelength of the incident light. Further, it is well known in the field that the lens of an optical device can made of a material having a temperature coefficient of expansion. Likewise, it is well known in the field that the face of any lens can be manufactured to be reflective, anti-reflective, partially reflective, transmissive or scattering to any degree.
Light-Emitting Diodes (LEDs), in particular High-Brightness LEDs (HBLEDs), produce a large amount of white light, on the order of about 100-200 lumens for commercial devices, with great efficiency HBLEDs are becoming more affordable and have the capacity to replace conventional light bulbs and compact fluorescent lighting in everyday use. HBLEDs are small, but not point-source, light emitters, often having a light-emitting area on the order of about 1 square millimeter. HBLEDs are generally robust and are constructed to survive relatively rough, harsh conditions, unlike conventional light bulbs and compact fluorescent lighting. Emission of light by HBLEDs is Lambertian, and as such they emit light in all directions. Further, the emissions from HBLEDs are complicated by reflections in the adjacent features of the HBLED package which must be considered. Harnessing the powerful emissions of light from HBLEDs can aid in the realization of greater efficiency and productivity in lighting.
The use of standard lenses and reflectors to optimize the emission of light from LEDs and other broad or extended distribution light sources has not satisfied the full potential. The methods for harnessing the emitted light from an LED generally fall into one or more of three categories; refractive, reflective and TIR reflective. Refractive lenses are molded around an LED according to the standard lens equation. Reflective devices use parabolic reflectors, with a light emitter at the center, to direct light. FIG. 1c shows a standard reflector lens of the prior art. The standard reflector lens 13 has light source 5, curved wall 14 and, in some cases, flat top surface 15 to prevent dirt and other contaminants from entering the optics. Total Internal Reflection (TIR) devices use a similar parabolic reflection system, but use a TIR parabolic reflector called a TIR lens. FIG. 1d shows a standard TIR lens of the prior art. The standard TIR lens 16 has light source 5, straight wall 17 and flat top surface 18.
In order to capture the maximum amount of emission, lenses for HBLEDs must be in close proximity to the HBLED. HBLEDs, having Lambertian emission, radiate in all directions. A lens or other optic device that is situated too far from an HBLED, and therefore outside of intimate contact, will not properly capture all of the emission. Lenses for HBLEDs are generally situated on the order of about 1 to 3 millimeters from the light source. Standard lenses of the prior art generally have a slow, circular variation, as shown in FIGS. 1a and 1b. This form is very limiting and not conducive to the broader area light emission of the HBLED. The nature of the HBLED light source is such that a regular, slow, circular variation in a lens will not adequately reflect or refract the light from a position on the light source other than the singular point to which the lens is trained. The wide source of light cannot be properly accommodated by the standard lens form.
In the example of the reflective device using a parabolic reflector, light is well-concentrated in the center beam. Around the beam, however, exists a broad roll-off zone. In this roll-off zone, light of a much lower intensity is distributed. This roll-off zone consists of light that is not being used to more efficiently illuminate the center beam, nor is it bright enough to properly illuminate the surrounding zone. It is wasted light.
Because LEDs are not point light sources, the standard lens equation is limited in its usefulness for illumination applications with LEDs. The standard lens is too spherical; only the light from the center point of the lens is optimized. Faster and more specialized spatial variation is required to direct the broad portions of the LED emission. The same is true for all emitted radiation from other extended distribution sources.